Friction-reducing drill pipe component

ABSTRACT

The friction reducing drill pipe component in the form of a sub ( 10 ) is adapted to form part of a drill string. The sub ( 10 ) comprises a tubular mandrel ( 12 ) having first and second ends for connection to adjacent components of the drill string. A sleeve ( 18 ) is mounted on the mandrel ( 12 ), and first and second stops on the mandrel ( 16, 20 ) restrain the sleeve  18  against axial movement relative to the mandrel ( 12 ). One of the stops ( 20 ) is removable or retractable to permit the sleeve ( 18 ) to be removed over the first end of the mandrel.

This invention relates to a drill pipe component, and in particular to acomponent to be placed in a string of drill pipe to reduce the frictionbetween the string and the hole wall.

In industries where long holes or bores are drilled, such as the oil andgas exploration and extraction industries, the friction which occurs dueto contact between the drill string and the bore wall may result in asubstantial increase in the torque required to rotate the string and thedrill bit. Such contact also causes wear and damage to the steel casingused to line sections of the bore.

In an effort to avoid these difficulties there have been variousproposals for friction reducing components to be mounted in or on thestring. U.S. Pat. No. 5,261,498 (The Red Baron (Oil Tools Rental)Limited) describes a typical friction reducing component or sub, inwhich a bore wall contacting sleeve is mounted on the lower part of amandrel via bearings and is axially retained on the lower mandrel partbetween a shoulder and an upper mandrel part. While this and other subshave been used successfully in numerous operations, the cost andcomplexity of such subs has limited their widespread adoption and use.

It is among the objects of embodiments of the present invention toprovide a friction-reducing drill pipe component which is relativelysimple in construction and is thus less expensive to manufacture andmaintain.

According to the present invention there is provided a friction-reducingdrill pipe component for forming part of a drill string, the componentcomprising a tubular mandrel having first and second ends for connectionto adjacent components of the drill string, a sleeve mounted on themandrel, and first and second stops on the mandrel for restraining thesleeve against axial movement relative to the mandrel, at least thefirst stop being removable from the mandrel to permit the sleeve to beremoved over the first end of the mandrel.

In use, the major parts of the component may be disassembled simply byremoving the first stop and then lifting the sleeve over the first endof the mandrel. This contrasts with conventional arrangements in whichremoval of the sleeve, if possible, requires, for example, thedismantling of the mandrel or heat treatment and expansion of thesleeve. Thus, maintenance and repair of components made in accordancewith embodiments of the present invention is relatively simple and inmany instances may be carried out on-site at a drilling location.

The sleeve may be rotatable relative to the mandrel or may benon-rotatable on the mandrel. In this area, components or subs in whichthe sleeve is fixed relative to a mandrel are described as “rotating”subs, as the sleeve rotates in the bore with the drill string. If thesleeve is rotatable on the mandrel such subs are described as“non-rotating” subs, as the sleeve remains stationary relative to thebore.

In non-rotating subs, bearings may be provided between the sleeve andmandrel, or the sleeve and mandrel may define bearing surfaces. Wherebearings are provided these may be introduced into the gap between thesleeve and the mandrel through a port in the sleeve. Bearing lubricantmay be trapped between the mandrel and sleeve, however it is preferredthat the fluid in the bore provides the necessary lubrication, and tothis end the spacing of the stops may be selected to provide a flow pathbetween the stops and the sleeve ends. One of the upper stop and theupper end of the sleeve may be configured to permit flow of fluidtherebetween in the event that the contact between the sleeve and borewall causes the sleeve to be pushed upwardly into contact with the upperstop, for example the upper end of the sleeve or the stop may bescalloped. Alternatively, ports may be provided in the upper end of thesleeve.

Preferably, the first stop is in the form of a collar. The collar mayengage with a screw thread formed on the mandrel or may be retained onthe mandrel by releasable connectors. The releasable connectors may bein the form of bolts or pins or, most preferably, are in the form ofsprung pins or dogs which normally extend radially from the mandrel toengage and retain the collar. The collar may define ports therethroughto allow the dogs to be pushed inwardly to allow removal of the collar.The collar may also define slots in communication with the ports so thatthe collar may be rotated to cover the pins. Where sprung dogs areutilised to retain the sleeve, the dogs may be pushed inwardly to permitremoval of the sleeve. Thus, with this embodiment of the invention it ispossible for unskilled personnel to remove and replace the sleeve usingonly very simple tools, such that components may be repaired on-sitewithout requiring specialised assistance or equipment.

Preferably also, the second stop is in the form of a stop ring. The ringmay be removable but is preferably integral with the mandrel. In thepreferred embodiment the mandrel, the mandrel end connections and thesecond stop are machined from a single piece of metal. The first stopand the sleeve may each also be formed of single pieces of metal.Accordingly, the resulting connector has only a small number of partsand is therefore easily assembled and disassembled and may be of robustconstruction.

The sleeve may have a cylindrical outer surface, or may define axial orhelical blades with slots therebetween, to facilitate passage ofdrilling fluid through the annulus between the drill string and the borewall. The blades may be of resilient material, such as PTFE, PEEKpolymeric material, or vulcanised neoprene, most preferably reinforcedwith metal or some other rigid structure. Alternatively, the blades maybe of metal, such as steel or alloy. The metal blades may be integralwith the sleeve or welded or otherwise bonded to the sleeve. The slotsmay be undercut.

According to another aspect of the present invention there is provided afriction-reducing drill pipe component for forming part of a drillstring, the component comprising a tubular mandrel having first andsecond ends for connection to adjacent components of the drill string,and a sleeve mounted on the mandrel, the sleeve defining external bladeswith undercut channels therebetween.

According to a further aspect of the present invention there is provideda friction-reducing drill pipe component for forming part of a drillstring, the component comprising a tubular mandrel having first andsecond ends for connection to adjacent components of the drill string, asleeve mounted on the mandrel, and spring-mounted lock dogs mounted onthe mandrel and operatively associated with the sleeve for releasablyretaining the sleeve on the mandrel.

These and other aspects of the present invention will now be described,by way of example, with reference to the accompanying drawings, inwhich:

FIG. 1 is a part-sectional view of a friction-reducing drill pipecomponent in accordance with a first embodiment of the presentinvention;

FIG. 2 is a part-sectional view of a friction-reducing drill pipecomponent in accordance with a second embodiment of the presentinvention;

FIG. 3 is a sectional view of the mandrel of the component of FIG. 2;

FIG. 4 is a sectional view on line 4—4 of FIG. 2;

FIG. 5 is a part-sectional view of a friction-reducing drill pipecomponent in accordance with another embodiment of the presentinvention;

FIG. 6 is a sectional view of the mandrel of the component of FIG. 5;

FIG. 7 is a perspective view of the sleeve of the component of FIG. 5;and

FIG. 8 is a perspective view of an alternative sleeve for the componentof FIG. 5.

Reference is first made to FIG. 1 of the drawings, which illustrates afriction-reducing drill pipe component in the form of a sub 10 formingpart of a drill string (not shown) for location in a drilled bore. Thesub 10 comprises a tubular body or mandrel 12 provided with conventionalconical threaded pin and box connections 14, 15 to permit the sub 10 toform part of a drill string. A stop ring 16 is formed on the mandrel 12and locates the lower end of a sleeve 18. The upper end of the sleeve 18is located by a stop comprising a set of sprung lock dogs 20 biassed toextend radially from the mandrel 12 into corresponding slots 22 definedon the inner surface of the sleeve 18. In this embodiment the sleeve isa “rotating” sleeve, in that it rotates with the mandrel 12.

To remove the sleeve 18 from the mandrel 12 an operator depresses thelock dogs 20 by pushing on the lock dogs 20 through the sleeve ports 24which communicate with the slots 22. When the lock dogs 20 are pushedinwardly the sleeve 18 may be lifted over the depressed dogs 20, andremoved from the end of the mandrel.

Reference is now made to FIGS. 2, 3 and 4 of the drawings, whichillustrate a friction-reducing pipe component in the form of a sub 30 inaccordance with a further embodiment of the present invention. The sub30 is somewhat similar to the sub 10 described above, in that itcomprises a tubular mandrel 32 defining corresponding pin and boxconnections 34, 35 and carrying a stop ring 36 to retain a sleeve 38 onthe mandrel 32. Further, the upper end of the sleeve 38 is retained bylock dogs 40. However, the lock dogs 40 engage with a lock collar 41rather than with the sleeve 38, which is thus free to rotate on themandrel 32. Those working in the area would describe the sleeve 38 as ofthe “non-rotating” type, as in use the sleeve 38 remains stationaryrelative to the bore wall, while the mandrel 32 and the remainder of thedrill string rotates.

The lock dogs 40 engage slots 42 in the collar 41, and ports 44 provideoperator access to the lock dogs 40. Each port 44 is located at one endof the respective slot 42, such that the collar 41 may be rotated on themandrel 32 until the dogs 40 engage the other “closed” end of the slot42. Of course the ports 44 and slots 42 are arranged such that rotationof the sub 30 in a bore tends to result in rotation of the collar 41 tobring the dogs 40 to the closed ends of the slots 42.

The lock dogs 40 are illustrated in greater detail in FIG. 4 of thedrawings. Each lock dog 40 is located in a respective threaded hole 46which accommodates a stepped and threaded lock dog retainer 48. A largerdiameter stop 50 is provided on each lock dog 40 to engage a retainershoulder 52 and limit the outward radial extension of the dog 40. Acompression spring is provided between each lock dog and the base of thehole 46, to urge the dog radially outwardly. The dogs 40 are ported toprevent the dogs being pushed inwardly by the elevated pressuresexperienced downhole.

In use, a number of subs 30 will be provided in a drill string, and asthe string is rotated in a bore the sleeve 38, which is of largerdiameter than the other parts of the drill string, will contact thecasing which lines the bore and the mandrel 32 will rotate relative tothe non-rotating sleeve 38. In this particular embodiment the mandrel 32and the sleeve 38 each define plane bearing surfaces, howeverlubrication is provided by the drilling mud which, during a drillingoperation, will flow upwardly through the annulus between the sub 30 andthe bore casing. This drilling mud will find its way between the stopring 36 and the lower end of the sleeve 38, pass between the mandrel andthe sleeve, and then flow out between the upper end of the sleeve 38 andthe collar 41. To ensure that the fluid may flow out between the upperend of the sleeve 38 and the collar 41, the collar 41 is scalloped.

From FIG. 3 of the drawings it will be noted that the mandrel 32 andstop ring 36 are formed from a single piece of metal. Further, thesleeve 38 and collar 41 are also each formed of a single piece of metal.The sub 30 is therefore very robust, and tests have revealed that thevarious parts of the sub 30 experience very little wear under normalcircumstances. However, if it is desired to remove the sleeve 38 fromthe mandrel 32, this is achieved by depressing the lock dogs 40 to allowremoval of the collar 41, and then depressing the lock dogs to allowremoval of the sleeve 38 from the end of the mandrel. Similarly, thesleeve 38 may be refitted on the mandrel 32 with equal ease.

Reference is now made to FIGS. 5, 6 and 7 of the drawings whichillustrate a friction-reducing drill pipe component in the form of a sub60 in accordance with a further embodiment of the present invention. Thesub comprises a tubular mandrel 62 provided with conventional pin andbox connections 64, 65 to permit the sub 60 to form part of a drillstring. The mandrel also defines a stop ring 66 which locates the lowerend of a sleeve 68, the upper end of the sleeve 68 being located by acollar 70 which engages a thread 72 cut on the outer surface of themandrel 62. Like the sub 30 described above, the sleeve 68 is rotatableon the mandrel 62, and in this embodiment various bearings 74 areprovided between the sleeve 68 and the mandrel 62, the opposing faces ofwhich are shaped to define appropriate bearing races or tracks 76, 77(it should be noted that the dimensions of the bearings 74 and thetracks, 76, 77 are shown somewhat exaggerated in the Figures).

Reference is now made in particular to FIG. 7 of the drawings, whichillustrates the sleeve 68. It will be noted that the sleeve 68 definesfour axially extending blades 78 with channels or slots 80 therebetween.The blades 78 are formed of steel, a metal alloy or a resilientmaterial, such as PTFE, moulded or otherwise formed or secured around asteel reinforcing body. To facilitate assembly and disassembly of thesub 60, various ports 82 are provided in the sleeve 68 to allow bearingsto be placed in or removed from the appropriate bearing tracks 76, 77between the mandrel 62 and the sleeve 68.

To disassemble the sub 60, the ports 82 are opened and the bearings 74removed therethrough. The collar 70 is then disengaged from the thread72 and removed from the mandrel 62. The sleeve 68 may then be liftedover the upper end of the mandrel 62. To reassemble the sub 60 thesesteps are simply repeated in the reverse order.

Reference is now also made to FIG. 8 of the drawings, which illustratesan alternative sleeve 88 defining three helically extending blades 90with undercut channels 92 extending therebetween; the undercut channels92 provide a larger flow area between the blades 90 while not reducingthe contact area provided by the blades 90.

It will be clear to those of skill in the art that the above-describedembodiments are merely exemplary of the present invention, and thatvarious modifications and improvements may be made thereto, withoutdeparting from the scope of the present invention. In a furtherembodiment, the sub 30 described above may be modified by the provisionof a sleeve defining a series of blades, and in a still furtherembodiment the sleeve may include means to permit for filling of the gapbetween the sleeve 38 and the mandrel 32 with bearings, which may be inthe form of a large number of glass balls.

What is claimed is:
 1. A friction-reducing drill pipe component forforming part of a drill string, the component comprising a tubularmandrel having first and second ends for connection to adjacentcomponents of a drill string, a sleeve mounted on the mandrel, and firstand second stops on the mandrel, intermediate the first and second ends,for restraining the sleeve against axial movement relative to themandrel, at least the first stop being movable to a retracted positionwhile retained on the mandrel, wherein an outermost diameter describedby the first stop in the retracted position and the mandrel incombination is less than an inner diameter of the sleeve to permit thesleeve to be removed over the first end of the mandrel.
 2. The componentof claim 1, wherein the sleeve is rotatable relative to the mandrel. 3.The component of claim 2, wherein the sleeve and mandrel define bearingsurfaces.
 4. The component of claim 2, wherein bearings are providedbetween the sleeve and mandrel.
 5. The component of claim 4, wherein thebearings are introduced into a gap between the sleeve and the mandrelthrough a port in the sleeve.
 6. The component of claim 2, wherein atleast one opening is provided in one of the sleeve and mandrel to permitdrilling fluid in the bore to enter a gap between the sleeve and mandreland serve as a lubricant therebetween.
 7. The component of claim 6,wherein the spacing of the stops and the length of the sleeve areselected to provide a flow path between the stops and the sleeve ends.8. The component of claim 7, wherein one of said first stop and saidfirst end of the sleeve is configured to permit flow of fluidtherebetween in the event that the contact between the sleeve and borewall and downward movement of the drill string relative to the bore wallcauses the sleeve to be pushed upwardly into contact with the firststop.
 9. The component of claim 8, wherein the first stop is scalloped.10. The component of claim 1 wherein the first stop is in the form of acollar.
 11. The component of claim 10, wherein the collar is retained onthe mandrel by therefore retracted connectors.
 12. The component ofclaim 11, wherein the connectors are sprung dogs which normally extendradially from the mandrel to engage and retain the collar.
 13. Thecomponent of claim 11, wherein the collar further defines ports formedtherethrough to permit access to the connectors.
 14. The component ofclaim 13, wherein the collar further defines slots in communication withthe ports so that the collar may be rotated to cover the connectors. 15.The component of claim 1, wherein the second stop is in the form of astop ring.
 16. The component of claim 15, wherein the stop ring isintegral with the mandrel.
 17. The component of claim 16, wherein themandrel, the mandrel ends and the second stop are machined from a singlepiece of metal.
 18. The component of claim 1 wherein the first stop andthe sleeve are each formed of single pieces of metal.
 19. The componentof claim 1 wherein the sleeve has a cylindrical outer surface.
 20. Theconnector of claim 1, wherein the sleeve carries external blades withslots therebetween.
 21. The connector of claim 20, wherein at least theblade surfaces are of resilient material.
 22. The connector of claim 20,wherein the slots are undercut.
 23. A friction-reducing drill pipecomponent for forming part of a drill string, the component comprising atubular mandrel having first and second ends for connection to adjacentcomponents of a drill string, a sleeve mounted on the mandrel, andspring-mounted lock dogs mounted on the mandrel and operativelyassociated with the sleeve for releasably retaining the sleeve on themandrel, the released sleeve being removable over the first end of themandrel.
 24. A friction-reducing drill pipe component for forming partof a drill string, the component comprising a unitary tubular mandrelhaving first and second ends for connection to adjacent components of adrill string, a sleeve directly mounted on the mandrel, first and secondstops on the mandrel for restraining the sleeve against axial movementrelative to the mandrel, at least the first stop being moveable to aretracted position while being retained on the mandrel, wherein anoutermost diameter described by the first stop in the retracted positionand the mandrel in combination is less than an inner diameter of thesleeve to permit the sleeve to be removed from the mandrel, the sleevebeing rotatable relative to the mandrel, and the sleeve and the mandreleach defining plane bearing surfaces.
 25. A friction-reducing drill pipecomponent for forming part of a drill string, the component comprising atubular mandrel having first and second ends for connection to adjacentcomponents of a drill string, a sleeve mounted on the mandrel, and firstand second stops on the mandrel, intermediate the first and second ends,for restraining the sleeve against axial movement relative to themandrel, at least the first stop being movable to a retractable positionwherein an outermost diameter described by the first stop in thenon-operative position and the mandrel in combination is less than aninner diameter of the sleeve to permit the sleeve to be removed over thefirst end of the mandrel, and wherein the sleeve is rotatable relativeto the mandrel and bearings are introduced into a gap between the sleeveand the mandrel through a port in the sleeve.
 26. A friction-reducingdrill pipe component for forming part of a drill string, the componentcomprising a tubular mandrel having first and second ends for connectionto adjacent components of a drill string, a sleeve mounted on themandrel, and first and second stops on the mandrel, intermediate thefirst and second ends, for restraining the sleeve against axial movementrelative to the mandrel, at least the first stop being movable to aretractable position wherein an outermost diameter described by thefirst stop in the non-operative position and the mandrel in combinationis less than an inner diameter of the sleeve to permit the sleeve to beremoved over the first end of the mandrel, and at least one opening isprovided in one of the sleeve and mandrel to permit drilling fluid inthe bore to enter a gap between the sleeve and mandrel and serve as alubricant therebetween.
 27. The component of claim 26, wherein thespacing of the stops and the length of the sleeve are selected toprovide a flow path between the stops and the sleeve ends.
 28. Thecomponent of claim 27, wherein one of said first stop and said first endof the sleeve is configured to permit flow of fluid therebetween in theevent that the contact between the sleeve and bore wall and downwardmovement of the drill string relative to the bore wall causes the sleeveto be pushed upwardly into contact with the first stop.
 29. Thecomponent of claim 28, wherein the first stop is scalloped.
 30. Afriction-reducing drill pipe component for forming part of a drillstring, the component comprising a tubular mandrel having first andsecond ends for connection to adjacent components of a drill string, asleeve mounted on the mandrel, and first and second stops on themandrel, intermediate the first and second ends, for restraining thesleeve against axial movement relative to the mandrel, at least thefirst stop being movable to a retracted position wherein an outermostdiameter described by the first stop in the retracted position and themandrel in combination is less than an inner diameter of the sleeve topermit the sleeve to be removed over the first end of the mandrel,wherein the first stop is in the form of a collar retained on themandrel by retractable connectors.
 31. The component of claim 30,wherein the connectors are sprung dogs which normally extend radiallyfrom the mandrel to engage and retain the collar.
 32. The component ofclaim 30, wherein the collar further defines ports formed therethroughto permit access to the connectors.
 33. The component of claim 32,wherein the collar further defines slots in communication with the portsso that the collar may be rotated to cover the connectors.